The invention relates to a process and apparatus for the manufacture of shaped bodies from silicon granulates for producing silicon melts.
The use of silicon in granular form as the starting material for silicon melts is known. The silicon granulate is placed in suitable receptacles and, by supplying energy, for example by means of resistance, induction, or radiation heating, it is brought to the melting temperature and converted directly into the molten state. In this manner there may be produced, for example, silicon melts for crucible drawing according to Czochralski (cf., for example, U.S. Pat. No. 4,330,362), for the manufacture of from coarse grained to monocrystalline sheets of silicon (cf. U.S. Pat. No. 4,447,829), for drawing silicon strips (cf., for example, U.S. Pat. No. 4,428,783) or for casting silicon blocks of columnar structure (cf., for example U.S. Pat. No. 4,175,610).
The use of silicon in granular form has a number of advantages over the equally feasible melting of lumps of material. For example, silicon granulates can be handled, transported, metered or charged, and optionally subsequently charged, without a great deal of apparatus. A disadvantage is the oxygen content, which results from the unavoidable oxide film on the particles, and occurs at a high level because of the large surface area of the granulate. In addition, it is virtually impossible to avoid the occurrence of extremely troublesome dusts in the melting zone. Furthermore, during the additional charging of silicon melts, relatively large chunks can cause splashes and disturbances in the melt as a result of vibration, or unreliable temperature changes, including those leading to partial solidification, can occur.
It is therefore an object of the invention to provide a process and apparatus for producing silicon melts using silicon granulates as the starting material without the occurrence of the above-mentioned disadvantages.